The present invention relates to a method of forming a contact configuration for soldering a metal connection on a region of a surface of a semiconductor body, the said body comprising a zone of a given conductivity type which adjoins the said surface according to the said region, said method mainly comprising the provision by serigraphy on at least a part of the said region of a conductive paste which, in particular in a vitrifiable phase, comprises at least a metal which is finely divided and a doping element which has the same conductivity type, the said paste is then vitrified thermally in such circumstances that the said dopant migrates in at least a surface part of the said region.
The present invention also relates to making a contact on the rear face of semiconductor solar cells and to the cells obtained by means of the method.
It is known that nowadays intensive investigations are performed in numerous laboratories to find means to reduce the cost of photovoltaic solar generators. Besides the high prices of the semiconductor material itself, certain steps in the manufacture of the solar cells prevent a price reduction if the methods used nowadays are maintained. This applies in particular to the step of making contact on each face of the cells, which is carried out by deposition by evaporation in a vacuum according to tested techniques which are adapted to applications of solar energy in space.
The replacement, whenever possible, of the said evaporation technique which is considered to be too expensive by a technique which can be automated more easily and operates with less expensive materials is considered as a measure of industrial and economical value by those skilled in the art. It is known that the use of conductive pastes which are provided on solar cells by serigraphy could form a solution to the problem called for especially from a point of view of the endeavored saving. For example, the article by M. B. Field and L. R. Scudder issued after the 12th Conference of Specialists of Photovoltaic Energy in Baton Rouge--United States--IEEE Proceedings 1976, p. 303--deals with investigations carried out in this direction. The method which consists of forming a contact on a region of the surface of a semiconductor body, for example, on the rear face of a solar cell (that is to say the face opposite to the photo-sensitive face) by use of the serigraphy technique involves numerous difficulties, including the difficulty of the subsequent soldering to a connection lug when a high percentage of the dopant is introduced in the conductive paste, or the non-ohmic character of the contact with high contact resistance when a comparatively low percentage of the said dopant is introduced in the said paste.
Another difficulty, found by applicants, is that the presence of the dopant in the vitrified deposit of the contact exerts an adverse influence. The mechanical behavior of a connection soldered to the vitrified deposit decreases in a non-acceptable manner when the device is exposed to environmental stresses. The life expectancy of the solar energy generator forms a factor which is indispensible and hence of great importance.